Classifications

• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08F—MACROMOLECULAR COMPOUNDS OBTAINED BY REACTIONS ONLY INVOLVING CARBON-TO-CARBON UNSATURATED BONDS
  • C08F279/00—Macromolecular compounds obtained by polymerising monomers on to polymers of monomers having two or more carbon-to-carbon double bonds as defined in group C08F36/00
  • C08F279/02—Macromolecular compounds obtained by polymerising monomers on to polymers of monomers having two or more carbon-to-carbon double bonds as defined in group C08F36/00 on to polymers of conjugated dienes

Definitions

• the present invention relates to thermoplastic compositions utilizing polymers of monovinylaromatic compounds which have been modified with rubber to increase their impact strength and which are particularly useful for manufacturing articles requiring increased environmental stress crack resistance (ESCR). More particularly, the present invention discloses a high impact polystyrene (HIPS) material which is particularly advantageous for use in food product containers which are normally subject to environmental stress cracking.
• HIPS high impact polystyrene
• rubber-reinforced polymers of monovinylidene aromatic compounds such as styrene, alphamethyl styrene, and ring-substituted styrenes are desirable for a variety of uses. More particularly, rubber-reinforced polymers of styrene having included therein discrete particles of a cross-linked rubber, for example, polybutadiene, the discrete particles of rubber being dispersed throughout the styrene polymer matrix, can be used in a variety of applications including refrigerator linings, packaging applications, furniture, household appliances, and toys.
• the conventional term for such rubber-reinforced polymers is "High Impact Polystyrene" or "HIPS".
• HIPS The physical characteristics and mechanical properties of HIPS are dependent upon many factors, including the particle size of the cross-linked rubber particles.
• One of the most important characteristics of HIPS material is the ability of such material to resist environmental stress cracking. This ability must be coupled with a high impact strength in order to be desirable for use in articles such as food containers.
• other such properties which must be maintained for such articles include tensile strength and material gloss.
• ESCR environmental stress crack resistance
• thermoplastic polymers utilized in food containers are particularly important.
• Articles made from styrene polymers modified to increase impact strength are prone to stress cracking when they come into contact with common agents found in organic food products such as fats and oils.
• organic blowing agents such as halohydrocarbons, containing fluorine and chlorine.
• HIPS material was manufactured utilizing a high molecular weight material having a stated molecular mass of at least 300,000, a viscosity greater than or equal to 140 centipoise, containing between 7 and 10% by weight of rubber, and the polymerization being carried out in the presence of alphamethyl styrene dimer or a compound chosen from n-dodecylmercaptan, tertiarydodecylmercaptan, diphenyl 1,3 butadiene, or various other compounds or mixtures thereof.
• this process was carried out in the presence of cyclohexane and ethylbenzene equal to at least 7% by weight of the total ingredients.
• additives including monotriglycerides of stearates from polyethylene waxes were also necessary.
• the present invention overcomes the disadvantages of the known high impact polystyrene materials by providing a polystyrene material blended with a high molecular weight rubber requiring no additional additives or lubricants.
• the high impact polystyrene disclosed by the present invention demonstrates a high resistance to environmental stress crack resistance, high impact strength, good tensile strengh, and good gloss.
• the present invention discloses a thermoplastic composition containing a polymer of a monovinylaromatic compound which has been modified with a rubber to increase its impact strength and environmental stress crack resistance, which compound was obtained by polymerizing the monovinylaromatic material in the presence of the rubber.
• the proportion of the soft component in the polymer, which has been modified to increase the impact strength is less than 27% by weight based on the polymer, the soft component being defined as the toluene-insoluble constituent of the polymer which has been modified to increase its impact strength, minus any pigment which may be present.
• the particular rubber utilized in the present invention should be of a high molecular weight and preferably is of the type sold by Firestone and designated as Firestone 7345 or "Diene 70" having a Mooney viscosity of approximately 70, a numerical molecular weight of about 146,000, a weight average molecular weight of about 337,000, and a Z molecular weight of about 630,000 as measured by the gel permeation technique.
• the high impact polymers may be manufactured in accordance with any conventional process, provided the constituents mentioned hereinabove are utilized.
• Normal manufacturing processes include mass polymerization and solution polymerization such as that disclosed in U.S. patent 2,694,692 or mass suspension polymerization such as that disclosed in U.S. patent 2,862,906.
• Other processes of manufacture may also be used, provided the processes are capable of utilizing the constituents mentioned herein.
• Suitable monovinylaromatic compounds utilizing the present invention include styrene as well as styrenes alkylated in the nucleus or side-chain such as alphamethylstyrene and vinyltoluene.
• the monvinyl-aromatic compounds may be employed singly or as mixtures.
• styrene was the monovinylaromatic compound of preference.
• the high impact polystyrene manufactured according to the present invention is formed by polymerizing the monovinylaromatic compound in the presence of the Diene 70 rubber.
• the polymerization is carried out in a conventional manner by mass polymerization, solution polymerization, or polymerization in aqueous dispersion, the rubber first being dissolved in the polymerizable monomer and this solution then being subjected to polymerization.
• the starting solution may be mixed with up to 50% by weight based on the monovinylaromatic compound employed of an inert diluent.
• Preferred inert diluents include aromatic hydrocarbons or mixtures of aromatic hydrocarbons such as toluene, ethylbenzene, xylenes, or mixtures of these compounds.
• the present invention may also be utilized in a continuous flow process for producing polystyrene utilizing a pre-inversion reactor in which a solution of styrene, polystyrene, and rubber are mixed prior to being introduced into a second stirred tank reactor.
• the viscosity of the solutions in the pre-inversion and in the second stirred tank reactor are closely controlled to produce desirable HIPS.
• the particular process for manufacturing the preferred embodiment may be found in U.S. patent 4,777,210, to Sosa, et al., dated October 11, 1988, the entire disclosure of which is hereby incorporated herein by reference.
• a mixture of conventional rubber having a molecular weight corresponding to a Mooney viscosity of approximately 50 was blended with a special rubber having a molecular weight corresponding to a Mooney viscosity of about 70 which was then processed into a high impact polystyrene material by the above-mentioned patented process.
• the finished product was then tested for environmental stress crack resistance, impact resistance, and gloss and the results appear in Table I hereinbelow.
• the particular rubber materials utilized were "Diene 55" a material manufactured by Firestone Tire and Rubber Company and designated as 7025, and “Diene 70", also manufactured by Firestone Tire and Rubber Company and designated as 7345. Both of these rubbers are of the polybutadiene type. It can be seen from Table I that the conventional rubber, "Diene 55", modified high impact polystyrene exhibits a much lower ESCR than the HIPS material manufactured from the blend of the Diene 70 material with the Diene 55 rubber.
• sample “A” represents a conventional HIPS material of straight 55 viscosity rubber at 6.6% by weight.
• the ESCR values are 36 and 3 for this material.
• Sample “B” is a HIPS material manufactured with slightly less rubber (6.5%) but at the higher viscosity (60).
• the resulting ESCR values for the higher viscosity material are significantly higher: 49 and 6.
• a high impact polystyrene material was made utilizing styrene monomer and a higher molecular weight rubber exhibiting a Mooney viscosity in the range of approximately 90.
• This HIPS material exhibited even greater environmental stress crack resistance than that utilizing the blended polybutadiene rubbers.
• the 90 viscosity high molecular weight polybutadiene was processed utilizing FDA-approved food-grade mineral oil to extend the polybutadiene and allow it to be processed.
• the HIPS material was manufactured according to the process set forth in the incorporated patent mentioned hereinabove.
• the oil-extended polybutadiene having a 90 Mooney viscosity was processed utilizing 15-20% mineral oil, by weight of the polybutadiene, prior to its incorporation the HIPS material through the process mentioned above.
• One particularly useful mineral oil is Britol, a white mineral oil manufactured by Petroleum Specialties International, Inc., of Perth Amboy, New Jersey. This oil-extended polybutadiene resulted in a HIPS material exhibiting a significant increase in the ESCR and acceptable levels of impact strength and gloss as illustrated in the following Table II.
• Table III shows the relationship of the numerical average molecular weight, the weight average molecular weight and the Z molecular weight for the polybutadiene materials utilized in the HIPS manufactured according to the present invention.
• Applicants have found that by utilizing a higher molecular weight rubber with gels below about 27%, improved ESCR properties can be obtained in the high impact polystyrene without loss of color or impact strength.
• a 60 Mooney viscosity blended polybutadiene in the HIPS material it has also been found advantageous to go as high as a 90 Mooney viscosity extended polybutadiene by extending the rubber with FDA-approved mineral oil to improve processing and allow use of a much higher molecular weight rubber in the HIPS formulation.
• the present invention discloses the use of a high molecular weight rubber as indicated by a Mooney viscosity and more particularly, a high molecular weight polybutadiene rubber with Mooney viscosities exceeding about 50, useful in preparing high impact polystyrene material utilizing gel levels below about 27% and exhibiting higher environmental stress crack resistance values than previously found in conventional HIPS manufacturing techniques.
• the present invention discloses the use of even higher molecular weight polybutadiene rubbers for manufacturing HIPS with gel levels below about 27% utilizing high Mooney viscosity rubbers which have been oil-extended by the use of FDA-approved mineral oil and which do not degrade the quality of the finished products such as food containers. While white mineral oils have been found useful in the present invention, other FDA-approved lubricants for incidental food contact could also be utilized to extend the high-viscosity rubber. The following criteria was used to pass or fail materials.
• the disperse phase or gel, consists essentially of particles of graft copolymers of the polybutadiene rubber and polymerized monovinylaromatic compound, plus mechanically occluded particles of the polymerized monovinyl-aromatic compound located in the rubber particles.
• Gel level may be measured as the toluene-insoluble component of the rubber-modified high-impact compound. Gel levels are indicated in weight percents.
• monovinylaromatic monomer or compound when referring to monovinylaromatic monomer or compound, it is intended that this include styrenes, alphamethyl styrene, and ring-substituted styrenes.
• rubber when referring to rubber it is intended that such phrase refer to natural rubber, polybutadiene, polyisoprene, and copolymers of butadiene and/or isoprene with styrene.
• ESCR values are determined according to the procedures set forth in the above-incorporated patent, US 4,777,210, at columns 10 and 11 thereof.
• Mooney viscosity is determined using the procedures set forth at pages 109 and 110 of RUBBER TECHNOLOGY , Third Edition, a publication sponsored by the Rubber Division of the American Chemical Society, and published by Van Nostrand Reinhold Compagny of New York.

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• Chemical & Material Sciences (AREA)
• Health & Medical Sciences (AREA)
• Chemical Kinetics & Catalysis (AREA)
• Medicinal Chemistry (AREA)
• Polymers & Plastics (AREA)
• Organic Chemistry (AREA)
• Compositions Of Macromolecular Compounds (AREA)
• Graft Or Block Polymers (AREA)
• Addition Polymer Or Copolymer, Post-Treatments, Or Chemical Modifications (AREA)
• Macromonomer-Based Addition Polymer (AREA)

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• 1991
  • 1991-05-20 KR KR1019910008285A patent/KR100217804B1/ko not_active Expired - Fee Related
  • 1991-05-21 AT AT91870083T patent/ATE157999T1/de active
  • 1991-05-21 ES ES91870083T patent/ES2109940T3/es not_active Expired - Lifetime
  • 1991-05-21 EP EP91870083A patent/EP0458773B1/de not_active Revoked
  • 1991-05-21 DE DE69127581T patent/DE69127581T2/de not_active Revoked
  • 1991-05-21 JP JP14417891A patent/JP3257683B2/ja not_active Expired - Fee Related
  • 1991-05-21 CN CN91103965A patent/CN1050368C/zh not_active Expired - Fee Related
  • 1991-05-21 TW TW080103934A patent/TW206978B/zh active

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